The present invention relates generally to a system for making frozen comestibles and the like having an over-run, and, more particularly, the invention relates to a system for making frozen desserts such as ice cream.
In the manufacture of frozen comestibles, the usual practice is to prepare a mix and provide over-run to the product by inclusion of air or inert gas, such as nitrogen, into the mix before entering a swept surface heat exchanger to chill or freeze the mix and provide a product with desired over-run. The heat exchanger is associated with a refrigeration system which connects to a manifold on the heat exchanger. In the normal functioning of the heat exchanger, the air or inert gas is distributed throughout the mix by a dasher resulting in a chilled or frozen product having over-run.
As used herein the over-run is specified as a percentage, by volume, increased by inclusion of air or inert gas. For example, if the mix is increased in volume by the inclusion of 20% of the mix volume of gas, it is said to have a 20% over-run. If equal volumes of mix and gas are included in the final product, it is said to have 100% over-run.
It has been common to introduce the mix into a gear pump which has an inlet for receiving air to provide the over-run. The combination of mix and air are then pumped into the swept surface heat exchanger. The gear pump has had a number of limitations and the heretofore known systems of providing for air injection into the mix have also had limitations so that there have been substantial variations in the over-run. Thus, these previously known systems have not provided consistency in over-run control in the manufacture of frozen comestibles, including frozen desserts, ice cream, sherbet, and the like. In the manufacture of these products it is desired to provide between 20% and 200% over-run.
In heretofore known systems, as indicated, it is usual to provide the pump for feeding the mix and gas to the swept surface heat exchanger but also to provide a pump at the outlet of the heat exchanger, thereby requiring multiple pumps. Further, heretofore known systems have required major changes, such as sprocket changes, to accommodate a wide range of over-run. In addition, in systems known before this invention, the amount of inclusion of air was subject to variations in line pressure.
The use of gear pumps in systems for manufacturing frozen comestibles also had limitations in providing desired control of the over-run. The gear pump is affected by the viscosity of the mix, and the mix temperature likewise affects the gear pump operation. Upstream and downstream pressure had an effect upon the operation of the gear pump as well. Further, the gear pump tends to wear because of gear meshing whereas it would be desirable to avoid this wear in the operation of the system.
The prior systems had difficulty with shut-downs occasioned by the need for terminating the output of the swept surface heat exchanger as might result from a problem in the product packaging line. It is difficult, in many prior systems, to effect start-up after such a shut-down.